The invention relates to a device for treating particulate product having a process chamber for receiving and treating the product, a bottom of the process chamber being constructed from baffle plates, that overlap each other, with slots formed between the latter through which the process air can be introduced into the process chamber with a substantially horizontal component of motion.
A device of this kind is known from EP 0 370 167 A1.
Devices of this kind are used to dry, granulate or coat particulate products.
A gaseous agent, known as process air, is introduced into the process chamber through the bottom, entering the process chamber through the numerous slots between the overlapping baffle plates in substantially horizontal direction.
In the case of the before-mentioned device the bottom consists of a ring of radially extending guide plates, that overlap each other, with the slots extending in radial direction. The product to be treated, placed on the bottom, is whirled up by the process air to form a toroidally rotating band. The bottom is annular in shape, i.e. comprises a centrally arranged displacement body. Due to its initial horizontally directed component of motion, the toroidally rotating band moves on a process air cushion. For spraying a desired agent on to the particulate product to be treated, nozzles may be arranged in the bottom between the baffle plates.
This technology is based on the principle that the process air must be introduced into the process chamber initially with a substantially horizontal component.
In a further device for treating particulate product, known from EP 0 436 787 A1, the process air is guided in such a way that it is imparted a substantially bottom-up, i.e. a substantially vertical flow direction already as it enters the process chamber. In the process chamber, there are provided longitudinally extending hollow lances which generally extend in cross-wise direction to the gas flow and which are provided with upwardly directed nozzles so that both the process air and the spraying direction of the nozzles follow a substantially vertical line of movement from the bottom toward the top. A device of that kind serves in particular for coating relatively coarse-grained products, for example pellets, in the pharmaceutical area.
The spectrum of particulate products to be treated is much broader in the case of the before-mentioned device according to EP 0 370 167 A1 than the spectrum of products that can be treated wit h the last-mentioned device.
Especially in applications in the fields of chemistry and pharmaceutical technology, the following essential criteria must be considered in connection with devices of that kind.
In order to meet the demands placed on hygiene, agreeable to contact and easy to clean surfaces should be provided.
The processes in the process chamber should be reproducible, which means that any functional contingencies must be excluded by suitable means.
A very e essential criterion is to be seen in what is known as xe2x80x9cscaling-upxe2x80x9d, i.e. the ability to enlarge the scale linearly while maintaining the specific process functions, such as the continuous recirculation and movement of the product according to an exactly defined pattern. Reverting to the rotating toroidal band produced in the device described first, this means that any scaling-up should only have the result to produce a rotating band of larger diameter, while the flow, particle and motion conditions prevailing in the band as such per volume unit should remain unchanged.
Further criteria are the best possible function of the device, achieved by giving the components a formal design adapted to the particularities of the product to be treated, in combination with the aerodynamic and thermodynamic aspects to be taken into consideration. In addition, an optimum design is to be achieved by suitable configuration both of the entire unit and of its details, in order to ensure agreeable handling, where form is function and function is form.
In the case of the device mentioned first, the product placed on the bottom can be lifted off the latter by the process air entering the system in horizontal direction and can be expanded to sort of an air bed.
However, the process air must of course eventually exit the rotating toroidal band, which ideally should occur without any outbursts or sort of volcanic eruptions of gas from the toroidal band. But finally there do not exist any defined breaking-up points for the moving product and/or any defined points of exit for the process air from the product. In order to achieve the best possible degree of uniformity in the drying process of the particulate product, especially in cases where a liquid sprayed from nozzles is to be applied as uniformly as possible on the product, that has been whirled up in the toroidal band, the nozzles must be distributed, statistically, in such a way that all breaking-up points, that may arise in statistical distribution, will be uniformly covered in statistical average.
A further considerable problem with respect to the design of the radial slots arises in connection with the scaling-up aspect. Viewed from the top, the different overlapping baffle plates are substantially trapezoidal in shape. Now, when the diameter of the bottom is very much enlarged for scaling-up purposes, the distance at the periphery between two slots following each other in the direction of flow is much smaller in the radially inner region than in the radially outer region. To say it in other words: A particle of the product circulating in the radially inner region is accelerated and whirled up by the process air, that enters through the next following slot, after a much shorter travel than a particle circulating in a radially outer region. In order to ensure improved uniformity of the conditions it is, therefore, necessary to impart to a particle, that revolves in a radially outer region, a higher circumferential speed in order to guarantee that it will be surrounded, accelerated and whirled up by new process air at the same point in time as a radially inner particle. This is effected by making the height of the air exit slots greater toward the outside so that more process air can enter through the slots in the radial outer region. But this necessarily has the effect that the baffle plates rise a little in radial direction toward the outside and that the outer edge, consequently, presents a mechanical obstacle to the revolving floating band. It is, however, desired to have the product band float on an air cushion in non-contact fashion. In order to form a closed ring, the individual baffle plates are obliquely inclined. This inclination, and the arrangement of the baffle plates in the form of a ring where each baffle plate overlaps the next following baffle plate, lead to a structure that exhibits relatively large openings in the area of the slots through which product may drop, which is undesirable.
In view of the criteria mentioned before and the disadvantages of the device described first, as regards the undefined breaking-up points and the difficulties in connection with the scaling-up aspect, it is the object of the present invention to overcome these advantages and to provide a device that allows a broad spectrum of particulate product to be optimally treated.
This object is achieved according to the invention by the fact that the slots are arranged in such a way that two opposite flows of incoming process air, being directed one toward the other and along a substantially horizontal path, meet along a breaking-up zone and are then deflected to form an upwardly directed, substantially vertical flow.
As the process air is introduced through the bottom with a substantially horizontal motion component, it is possible to initially build up an air cushion carrying the product that has been whirled up in the process chamber. By providing two substantially horizontal, opposite flows, directed one toward the other, a zone is created where the two flows meet and are forcedly deflected in vertical upward direction. Escaping toward the bottom is rendered impossible by the baffle plates of the bottom. One thus obtains a well-defined breaking-up zone for the product to be treated in which the process air rises or breaks up, thereby exiting from the particulate product. The process air, that rises in the breaking-up zone to the top in a defined way, entrains part of the product floating on it, which will however leave the process air, which escapes to the top after a relatively short travel, fall back to the bed of product floating above the bottom where it will be once more entrained and, consequently, recirculated by the oppositely directed horizontal flows. In the-area of the bottom, up to the breaking-up point, the product is subjected to well-defined uniform treating conditions that depend on, among other things, the quantity and speed of the process air being introduced and the distance between two successive slots. These conditions change abruptly only in the breaking-up zone where the process air escapes to the top in a defined way due to the substantially rectangular deflection.
Consequently, there is provided a relatively long defined and substantially horizontal path where the different particles can be treated with the process air under properly controllable and manageable conditions.
If, for example, the product is only to be dried, the necessary thermal energy can be transmitted to the product to be treated during that horizontal path to dry the product correspondingly. In the breaking-up zone the process air is then deflected abruptly in upward direction, with the effect that the product will be entrained, the process air will separate from the product after a certain travel and allow the product to drop back to the bottom where it can be subjected to a further drying process over a defined path.
If the product is to be granulated or coated, for example, then a corresponding agent can be supplied to the product in a defined way in the breaking-up zone, and the corresponding drying processes can then take place during the movement along the uniform horizontal and d defined path.
This embodiment now also permits unproblematic xe2x80x9cscaling-upxe2x80x9d because any linear enlargement of the bottom will not lead to changes in the flow conditions in the horizontal region. It will only be necessary in this case to provide a larger number of baffle plates and slots in successive arrangement. There will still exist a defined breaking-up zone, i.e. the zone in which the oppositely directed flows meet each other. Accordingly, neither the fluidic nor the fundamental structural conditions need to be changed for scaling-up, as was the case, for example, with the device described first, where the baffle plates had to be raised additionally toward the outside for scaling up purposes, so that they presented mechanical obstructions.
The height of the slot and/or the air gaps remains always the same so that there is no risk that large openings may be produced by the scaling-up process through which the product may drop to the bottom. Further, the baffle plates can be arranged horizontally and need not be inclined, which latter arrangement furthers a sliding movement of the resting product in the direction of the air gaps.
According to a further embodiment of the invention at least one nozzle, pointing in vertical upward direction, is arranged in the breaking-up zone.
This feature provides the advantage that the breaking-up zone, in which the substantially horizontal and oppositely directed flows hit upon each other and are deflected toward the top, is used for introducing liquids with which the product is to be treated. The vertically upward flow in the breaking-up zone, which results from the substantially horizontal flows hitting upon each other, exhibits a motion characteristic which is very similar to an atomizing cone expanding in trumpet-like shape, which characteristic is ideal for treating a product with an atomizing cone. Contrary to the device described first, where the nozzles are distributed statistically over the bottom, it is now possible to apply a liquid at a single, well-defined point, namely in the breaking-up zone, which is a considerable advantage under aspects of process and control technology.
According to a further embodiment of the invention, guide surfaces are arranged in the area of the breaking-up zone which define the transition from the horizontal flows to the vertically upward flows.
This feature provides the advantage that in the case of product sensitive to impact the directional change from the substantially horizontal direction to the vertically upward direction is gently assisted by mechanical means. Examples of such delicate products are relatively large pellets, as used in the pharmaceutical industry, that were obtained by granulation or compression and that exhibit relatively sharp edges and corners. Although it is the process air flows, not the product particles, that hit upon each other directly in the breaking-up zone, it cannot be excluded that individual particles may hit each other. If such particles were to hit each other from diametrically opposite directions, eruptions could take place. Such eruptions are not to be expected with relatively small and insensitive products so that in this case no such guide plates would have to be provided, though they may still be present in order to support the directional change.
According to a further embodiment of the invention, slots are arranged also in the area of the circumference of the bottom, through which process air can be introduced in line with the oppositely directed flows.
This feature provides the considerable advantage that no deposits are permitted to form in the circumferential corner region between the horizontal bottom and the upright tank wall. It has been observed that some sorts of products have the tendency to settle gradually in those corners and to thereby escape the further treatment. By arranging slots, through which process air enters the process chamber, also in this critical area, these critical corner points are now sort of continuously blown through.
According to a further embodiment of the invention, the breaking-up zone extends approximately centrally across the bottom.
This feature provides the advantage that the bottom is thereby divided into two mirror-symmetrical identical halves so that when the product eventually reaches the central breaking-up zone it has passed on both sides of that zone similar treating steps which were, in addition, carried out over traveling paths of equal length.
According to a further embodiment of the invention the slots extend along secants, and the breaking-up zone extends along a diameter, in a circular bottom.
In the case of such a design of the bottom or the process chamber the length of the secants increases continuously in radial direction from the outside toward the inside, which means that the space available for, and the process air that can be supplied to a given product quantity increases toward the breaking-up zone. To say it in other words, the product can sort of relax or breathe out, and the particles, having available increasingly more space, can permanently move away one from the other so that they can be optimally treated with the process air without hindering or influencing one another. It is only in the breaking-up zone that the particles meet again and are deflected vertically toward the top.
Other geometries than circular shapes are also possible, as for example square or rectangular shapes. If the breaking-up zone extends diagonally through a square, then the two oppositely directed areas are divided into triangles in which the product moves from the point toward the breaking-up zone.
However, there is also the possibility to give the bottom a rectangular shape and to arrange the slots in parallel to the short sides of the rectangle so that, depending on the length of the long sides of the rectangle, sufficient horizontally directed treating paths are available before the oppositely directed flows meet at the center of the breaking-up zone.
This provides the system-immanent possibility to use a plurality of different bottom geometries with the aim to create optimum conditions for the product to be treated at any time.
According to a further embodiment of the invention, two inflow chambers are arranged beneath the bottom, to which process air can be supplied.
This feature provides the advantage that the two inflow chambers can be used to build up, in a defined fashion, the oppositely directed flow components on both sides of the breaking-up zone orxe2x80x94to say it in other wordsxe2x80x94to supply the slots arranged on both sides of the breaking-up zone with process air via the two inflow chambers.
According to a further embodiment of the invention the two inflow chambers taper toward the breaking-up zone in vertical direction to a slot that opens directly adjacent the breaking-up zone.
This feature provides the advantage that the inflow chambers do not take up, structurally, the central space immediately below the breaking-up zone so that sufficient space is available in that area below the bottom to arrange other components, for example nozzles. Slots remote from the central breaking-up zone are supplied by the respective inflow chamber according to gas engineering principles. The orifices of the two inflow chambers immediately in front of the breaking-up zone provide the possibility to produce gas flows that meet each other at this point in an exactly defined way in order to form an upwardly directed vertical and central core flow. It is thus possible to produce a protective air cushion in the breaking-up region between the flows meeting each other.
According to further embodiment of the invention, the at least one nozzle is arranged between the divided inflow chambers, structurally separate from them.
This feature provides the advantage that inflow chambers and nozzles are each independent units which can be handled, for example cleaned, independently one from the other. This further opens up the possibility to pull off a nozzle, that might be blocked or clogged, for a short time during current operation and to clean it and mount it again without having to interrupt the process. And this because the two gas flows meeting each other form a continuous and tight gas shield that prevents any contamination from entering the process chamber during the short period of time needed for inspection purposes.
According to a further embodiment of the invention the at least one nozzle can be removed from the bottom from below.
This feature provides the advantage that the before-mentioned inspection, for example, can be carried out in a simple way also during operation of the system, by simply pulling such a nozzle off the bottom from below, or pivoting it away from the bottom in downward direction.
According to a further embodiment of the invention perforations are provided in the baffle plates approximately in their second half before the next slot, viewed in the flow direction of each oppositely directed partial flow exiting the slots.
This feature provides the advantage, especially in the case of relatively heavy and coarse particulate product, that the latter is imparted during the second half of its travel between two slots a certain vertical component in order to compensate for any dropping tendency caused by gravity so that even in the case of such critical products the latter will permanently float on an air cushion over a baffle plate between two successive slots.
According to a further embodiment of the invention the spacings between the slots, viewed in the direction of flow, are substantially equal.
This feature provides the advantage that these equal spacings produce very specific, defined treating conditions in the substantially horizontal partial flows which will be maintained also when the system is scaled-up, i.e. when a plurality of such uniformly spaced slots are arranged one behind the other.
It is understood that the features mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the context of the present invention.